Bioavailability and biogeochemical cycling of iron in glacially-influenced fjord systems of the high Arctic, Spitsbergen (Svalbard)

冰川产生的铁是大陆架水域潜在生物可利用铁的重要来源，但在很大程度上是不受限制的。这种微量营养素可能在沿海上升流区，特别是在大的北极大陆架上的初级生产力的施肥中发挥重要作用。更一般地说，在冰期-间冰期时间尺度和面对气候变化的情况下，冰川产生的铁可能是全球铁循环中一个至关重要的动态参与者。本项目以三个北极峡湾（斯匹次卑尔根、斯瓦尔巴群岛）铁的生物地球化学循环为目标，重点研究生物可利用铁的来源和跨峡湾系统的转移及其在峡湾沉积物中的成岩氧化还原循环。具体而言，我们计划验证以下假设：(1)冰川融水排放和冰川前径流带的冰川粉含有大量来自冰川碎屑冰下生物地球化学风化的生物可利用铁成分；(2)这些铁相输入峡湾，使水柱的初级生产力肥沃，并支持邻近峡湾沉积物中高速率的异化铁还原；(3)铁的底底循环，包括多个溶解和再氧化步骤，促进了活性铁相的运输，穿过峡湾到达河口，最终到达大陆架。为了实现我们的目标，我们将结合经典的（生物）地球化学分析，特别是孔隙水痕量金属测量和顺序铁提取方案，以及新开发的抗坏血酸提取方法，该方法专门针对水合铁，从而允许测定生物可利用铁含量，并分析铁同位素特征。

Glacially derived iron is an important, yet largely unconstrained source of potentially bioavailable iron to continental shelf waters. This micronutrient may play an important role in the fertilization of primary productivity in coastal upwelling areas particularly on the large Arctic shelf. More generally, glacially derived iron may be a vital and dynamic player in the global iron cycle over glacial-interglacial timescales and in the face of climate change. This project targets the biogeochemical cycling of iron in three Arctic fjords (Spitsbergen, Svalbard) with a focus on the sources and transfer of bioavailable iron across fjord systems and its diagenetic redox cycling in fjord sediments. Specifically, we plan to test the hypothesis that (1) glacial flour from glacial meltwater discharge and proglacial runoff zones contains a large bioavailable iron component deriving from subglacial biogeochemical weathering of glacial debris; (2) the input of these iron phases to the fjords fertilizes primary productivity in the water column and supports high rates of dissimilatory iron reduction in adjacent fjord sediments; and (3) the benthic cycling of iron, encompassing multiple dissolution and re-oxidation steps, facilitates the transport of reactive iron phases across the fjords to their mouths and ultimately to the shelf. To fulfill our objectives we will combine classical (bio)geochemical analyses, particularly pore-water trace metal measurements and sequential iron extraction schemes, with a newly developed ascorbic acid extraction method which specifically targets ferrihydrite and thus allows for the determination of the bioavailable iron content, and the analysis of iron isotope signatures.